Gas lasers, such as transversely excited gas lasers, which are operated at moderate to high pulse repetition rates require a means of recirculating the gas medium within the laser housing in order to replenish the gas medium within the discharge region. Previous methods of recirculating the gas have typically relied on various types of fans. These various types of fans have included tangential, vaneaxial and centrifugal blowers. One common characteristic of all of these fan types is the requirement of bearings which hold the fan in place while allowing the rotation of the fan at high speeds. These fans are typically employed within the laser housing itself, in order to recirculate the gas medium through the housing and, hence, through the discharge region between a pair of opposed laser electrodes. The ation of the recirculating fan serves to replenish the gas medium between successive electrode discharges, thus providing for a fresh supply of gas medium for each pulse.
The aforementioned bearings incorporated within these fans introduce a significant problem into the operation of such a laser, especially in the sealed type of recirculating gas laser. This problem is related to the requirement that the fan bearings include some type of lubrication in order to reduce the bearing friction. Inasmuch as the fan is within the sealed laser housing, the laser gas comes into contact with the bearing lubrication, thereby resulting in the contamination of the laser gas medium by the lubricant. Bearing particulate matter may also contaminate the gas medium. For those lasers which have an extended operational lifetime such a contamination of the laser gas medium may result in undesirable operating characteristics of the laser or the complete failure of the laser. This contamination of the gas medium has also been found to occur during the storage of such lasers during periods of nonuse.
Rotating fans also introduce other problems when employed in a gas laser. Because such fans are inherently magnetically driven devices requiring a DC or AC motor, they have a significant overall size and power consumption. They may also generate significant electromagnetic interference (EMI) and radio frequency interference (RFI) noise signals and are, typically, also a source of audible noise.